A large butterfly-shaped endocrine gland in the neck that produces hormones regulating growth, metabolism, and development; also, the adjective describing things related to this gland.
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Greek18th centurywell-attested
From ModernLatin thyreoides, from Greek thureoeides (θυρεοειδής), meaning shield-shaped, a compound of thureos (θυρεός, a large oblong shield) + eidos (εἶδος, form, shape). Thureos derives from thura (θύρα, a door), becausetheGreek oblong shield was shaped like a door — rectangular, in contrast to the round aspis. The thyroid cartilage of the larynx was named by Galen in the 2nd century
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Theword 'thyroid' ultimately comes from PIE *dhwer- (door) — the same root as English 'door,' German 'Tür,' and Latin 'foris' (door, which gave English 'foreign,' 'forest,' and 'forum'). The chain: PIE 'door' → Greek 'door' → 'door-stone' → 'large rectangular shield' (shaped like a door) → 'shield-shaped' → the thyroid gland. Your thyroid is, etymologically, named after a door.
thura (θύρα)(Greek (door — root of thureos, shield))foris(Latin (door, outdoors — PIE *dʰwer-))dor(Old English (door — same PIE *dʰwer-))Tür(German (door — same PIE root))dvāram(Sanskrit (door, gate — same PIE *dʰwer-))eidos (εἶδος)(Greek (form, shape — second element of compound))